Process for producing a polybenzoxazine monomer

ABSTRACT

A process for manufacturing a polybenzoxazine monomer, crosslinking the latter, and using the crosslinked product to form an ablative thermal protection system for a thruster nozzle or atmospheric reentry body.

TECHNICAL FIELD

The invention relates to a process for manufacturing a polybenzoxazinemonomer and crosslinking this monomer in order to form a crosslinkedproduct having improved charring and thermal stability properties. Thiscrosslinked product can in particular be used as an ablative resin forthe construction of a thruster nozzle or an atmospheric reentry body.

PRIOR ART

Ablative thermal protection systems of thruster nozzles or atmosphericreentry bodies are known to be made from phenolic resins synthesizedfrom formaldehyde and phenol, in order to obtain high aromatic andcrosslinking densities, and thus a high coke content, Formaldehyde andphenol are however compounds classified as carcinogenic, mutagenic andreprotoxic (CMR) category 1B and 2, whose use should be limited, inparticular to anticipate possible bans in the European Union.Furthermore, the reaction of phenol and formaldehyde is apolycondensation during which water is produced. This water can betrapped in the finished product, leading to a decrease in performance.In order to solve this problem, developments have been pursued to obtainablative resins by crosslinking benzoxazines. These developments reducewater entrapment in the finished product, but the solutions in theliterature, providing a finished product with thermal stability andcharring properties compatible with an application as an ablative resin,involve benzoxazines obtained by reaction of phenol with formaldehydeand an amine, and are therefore based on the use of compounds classifiedas CMR. Moreover, when these benzoxazines are synthesized withoutphenol, they exhibit poor thermal stability and charring properties.

It would therefore be desirable to have a new benzoxazine synthesispathway that limits the use of CMR compounds and avoids the use offormaldehyde in particular.

It would also be desirable to have a new synthesis pathway for materialsexhibiting thermal stability and charring properties adapted to theproduction of ablative thermal protection systems for thruster nozzlesor atmospheric reentry bodies.

DISCLOSURE OF THE INVENTION

The invention relates to a process for manufacturing a polybenzoxazinemonomer comprising condensing a polyamine of formula A with an aldehydeof formula B to obtain the polybenzoxazine monomer of formula C, thechemical formulas being provided below:

in these formulas:

N₁ is an integer greater than or equal to 2;

A₂ is selected from linear or branched, saturated or unsaturated,substituted or unsubstituted hydrocarbon chains interrupted by one ormore heteroatoms or by one or more saturated, unsaturated or aromatic,monocyclic or polycyclic, substituted or unsubstituted, carbocyclic orheterocyclic groups, or uninterrupted;

in formula A, the groups A₁ are identical or different and each have theabove formula A₁ with:

R₁ ^(a) is selected from: electron-withdrawing groups; saturated orunsaturated, substituted or unsubstituted, linear or branchedhydrocarbon chains comprising between 1 and 6 carbon atoms, optionallyinterrupted by one or more heteroatoms; substituted or unsubstituted,saturated, unsaturated or aromatic carbocyclic or heterocyclic groups;

n^(a) is an integer comprised between 0 and 2;

*-denotes the bond to A₂;

B₁ is selected from: saturated, unsaturated or aromatic, monocyclic orpolycyclic, substituted or unsubstituted carbocyclic or heterocyclicgroups; linear or branched, saturated or unsaturated, substituted orunsubstituted hydrocarbon chains, optionally interrupted by one or moreheteroatoms.

The invention provides a new polybenzoxazine synthesis pathway thatlimits the use of CMR compounds and avoids the use of formaldehyde inparticular. Furthermore, the product obtained by crosslinking thepolybenzoxazine monomer of formula C above has high thermal stabilityand charring properties, compatible with an application as an ablativeresin for thruster nozzles or atmospheric reentry bodies. In addition,the polybenzoxazine monomer of formula C has a liquid character atmoderate temperature and without resorting to an aromatic or halogenatedsolvent. It is therefore easily used in processes such as resin transfermolding (RTM).

In an example embodiment, A₂ is selected from linear or branched,saturated or unsaturated, substituted or unsubstituted hydrocarbonchains interrupted by one or more aromatic carbocyclic or aromaticheterocyclic groups.

Such a feature allows for improved conversion to the polybenzoxazinemonomer of formula C.

In particular, A₂ can be a substituted or unsubstituted xylylene group.

Such a feature further improves the conversion to the polybenzoxazinemonomer of formula C.

According to an alternative, A₂ can be selected from linear or branched,saturated or unsaturated, substituted or unsubstituted, uninterruptedhydrocarbon chains.

In an example embodiment, n^(a) is equal to 0.

In the alternative where n^(a) is non-zero, R₁ ^(a) can in particular beselected from: alkoxy groups; carboxyl groups; halogen atoms; saturatedor unsaturated, substituted or unsubstituted, linear or branchedhydrocarbon chains comprising between 1 and 6 carbon atoms, optionallyinterrupted by one or more heteroatoms; saturated, unsaturated oraromatic, substituted or unsubstituted carbocyclic or heterocyclicgroups.

In an example embodiment, the process can comprise, prior tocondensation, obtaining the polyamine of formula A, this obtainingcomprising:

-   -   an addition reaction of a polyamine of formula [NH₂]_(N1)-A₂        with an aldehyde of formula B2 to form an imine of formula A3,        and    -   a reduction reaction of the imine of formula A3 to the polyamine        of formula A, formulas B2 and A3 being provided below:

The amine of formula [NH₂]_(N1)-A is for example selected from thefollowing compounds: meta-xylylenediamine. The aldehyde of formula B2can, for example, be salicYlaldehyde.

The aldehyde of formula B can be a monoaldehyde, i.e., it can have onlyone aldehyde function.

In an example embodiment, B₁ is selected from substituted orunsubstituted monocyclic or polycyclic aromatic carbocyclic or aromaticheterocyclic groups.

The choice of such an aldehyde advantageously makes it possible toobtain, after crosslinking the polybenzoxazine monomer of formula C, aproduct with improved thermal stability and charring properties.

In particular, B₁ can be a substituted or unsubstituted benzene ring.

Alternatively, B₁ can be a linear or branched hydrocarbon chain. Thenumber of carbon atoms in this hydrocarbon chain can vary in largeproportions, B₁ can comprise between 1 and 20 carbon atoms or be apolymer.

In general, and whatever the example embodiment considered, N₁ can be aninteger equal to 2, In this case, the polyamine of formula A is adiamine. Alternatively, N₁ can take other values, in particular N₁ canbe equal to 3 or more.

Regardless of the embodiment considered, the condensation can be carriedout by bringing the mixture of the polyamine of formula A with thealdehyde of formula B to reflux. The condensation can be carried out intoluene, methanol, ethanol or without solvent.

The invention also relates to a process for manufacturing a crosslinkedproduct comprising crosslinking the polybenzoxazine monomer of formula Cobtained by carrying out the process described above.

This crosslinked product has a high coke content and high thermalstability, which makes it compatible with an application as an ablativeresin for manufacturing a thruster nozzle or an atmospheric reentrybody.

The crosslinking can be carried out by imposing a temperature greaterthan or equal to 130° C., for example comprised between 180° C. and 250°C.

In an example embodiment, there is crosslinking of a mixture comprisingthe polybenzoxazine monomer of formula C and an additionalmonobenzoxazine monomer of formula D, formula D being provided below:

formula in which:

R₁ ^(d) is selected from: substituted or unsubstituted furfuryl groups;saturated, unsaturated or aromatic, monocyclic or polycyclic,substituted or unsubstituted carbocyclic or heterocyclic groups;substituted or unsubstituted aralkyl groups; saturated or unsaturated,substituted or unsubstituted, linear or branched hydrocarbon chains,optionally interrupted by one or more heteroatoms or by one or moresaturated, unsaturated or aromatic, monocyclic or polycyclic,substituted or unsubstituted carbocyclic or heterocyclic groups;

R₂ ^(d) is selected from: electron-withdrawing groups; saturated orunsaturated, substituted or unsubstituted, linear or branchedhydrocarbon chains comprising between 1 and 6 carbon atoms, optionallyinterrupted by one or more heteroatoms; substituted or unsubstituted,saturated, unsaturated or aromatic carbocyclic or heterocyclic groups;

n^(d) is an integer comprised between 0 and 2;

D₁ is selected from: saturated, unsaturated or aromatic, monocyclic orpolycyclic, substituted or unsubstituted carbocyclic or heterocyclicgroups; linear or branched, saturated or unsaturated, substituted orunsubstituted hydrocarbon chains, optionally interrupted by one or moreheteroatoms.

The fact of adding the additional monobenzoxazine monomer of formula Dfurther facilitates the production of a liquid medium comprising thepolybenzoxazine monomer of formula C at moderate temperature and withoutresorting to an aromatic or halogenated solvent. This furtherfacilitates the use of the mixture in processes such as resin transfermolding (RTM) without significantly affecting the thermal and charringproperties of the resulting crosslinked product.

For example, it is possible to crosslink a mixture comprising thepolybenzoxazine monomer of formula C in an amount of 20% to 80% by massand preferably 20% to 50% by mass, and the additional monobenzoxazinemonomer of formula D in an amount of 20% to 80% by mass and preferably50% to 80% by mass.

In an example embodiment, D₁ is selected from substituted orunsubstituted monocyclic or polycyclic aromatic carbocyclic or aromaticheterocyclic groups.

In particular, D can be a substituted or unsubstituted benzene ring.

Alternatively, D₁ can be a linear or branched hydrocarbon chain. Thenumber of carbon atoms in this hydrocarbon chain can vary in largeproportions, D₁ can comprise between 1 and 20 carbon atoms or be apolymer.

R₁ ^(d) can in particular be selected from: substituted or unsubstitutedfurfuryl groups; substituted or unsubstituted monocyclic or polycyclicaromatic carbocyclic or heterocyclic groups; substituted orunsubstituted aralkyl groups. In particular, R₁ ^(d) can be asubstituted or unsubstituted furfuryl group. Alternatively, Rid is alinear or branched hydrocarbon chain. The number of carbon atoms in thishydrocarbon chain can vary in large proportions. R₁ ^(d) can, forexample, be a linear or branched hydrocarbon chain comprising between 1and 20 carbon atoms or be a polymer.

In an example embodiment, n^(d) is equal to 0.

In the alternative where n^(d) is non-zero, R₂ ^(d) can in particular beselected from: alkoxy groups; carboxyl groups; halogen atoms; saturatedor unsaturated, substituted or unsubstituted, linear or branchedhydrocarbon chains comprising between 1 and 6 carbon atoms, optionallyinterrupted by one or more heteroatoms; saturated, unsaturated oraromatic, substituted or unsubstituted carbocyclic or heterocyclicgroups.

The additional monobenzoxazine monomer of formula D can be obtained bycondensation between a monoamine of formula D2 below (having only oneamine function) with an aldehyde of formula D₁-CHO.

Alternatively, there is crosslinking of a mixture comprising thepolybenzoxazine monomer of formula C and an additional polybenzoxazinemonomer of formula E, formula E being provided below:

R₁ ^(e) is selected from: substituted or unsubstituted furfuryl groups;saturated, unsaturated or aromatic, monocyclic or polycyclic,substituted or unsubstituted carbocyclic or heterocyclic groups;substituted or unsubstituted aralkyl groups; linear or branched,saturated or unsaturated, substituted or unsubstituted hydrocarbonchains, optionally interrupted by one or more heteroatoms;

R₂ ^(e) is selected from: electron-withdrawing groups; saturated orunsaturated, substituted or unsubstituted, linear or branchedhydrocarbon chains comprising between 1 and 6 carbon atoms, optionallyinterrupted by one or more heteroatoms; substituted or unsubstituted,saturated, unsaturated or aromatic carbocyclic or heterocyclic groups;

n^(e) is an integer comprised between 0 and 2;

E₁ is selected from: saturated, unsaturated or aromatic, monocyclic orpolycyclic, substituted or unsubstituted carbocyclic or heterocyclicgroups; linear or branched, saturated or unsaturated, substituted orunsubstituted hydrocarbon chains, optionally interrupted by one or moreheteroatoms; and

N₂ is an integer greater than or equal to 2.

The fact of adding the additional polybenzoxazine monomer of formula Efurther increases the charring rate.

For example, it is possible to crosslink a mixture comprising thepolybenzoxazine monomer of formula E in an amount of 20% to 80% by mass,preferably 20% to 50% by mass, and the additional polybenzoxazinemonomer of formula C in an amount of 20% to 80% by mass, preferably 50%to 80% by mass.

Regardless of the embodiment considered, the proportion of additionalmonobenzoxazine monomer of formula D or additional polybenzoxazinemonomer of formula E can be selected so that the mixture is liquid whenheated to a temperature comprised between 20° C. and 100° C.

By way of example, each of R₁ ^(a), B₁, A₂. R₁ ^(d), R₂ ^(d), D₁, E₁, R₁^(e), R₂ ^(e) can be substituted with at least one of the followinggroups: hydroxymethyl, methyl, carboxylic acid.

The invention also relates to a process for manufacturing a thrusternozzle in which the nozzle is manufactured using a crosslinked productobtained by the process described above.

The thruster nozzle can be made of a composite material. In this case,the manufacture of the nozzle can comprise a first step of forming afibrous preform of the nozzle to be obtained impregnated by thepolybenzoxazine monomer of formula C obtained as described above or by amixture comprising this monomer as described above. This manufacture canfurther comprise a second step of heat treatment of the impregnatedfibrous preform so as to crosslink the polybenzoxazine monomer offormula C or the mixture and obtain the thruster nozzle.

The fibrous preform can, for example, comprise fibers of carbon, silica,glass or a ceramic material, such as silicon carbide. The fibrouspreform intended to form the fibrous reinforcement of the nozzle can beformed in various ways (draping of pre-impregnated fabric layers, forexample). In particular, impregnated two-dimensional orthree-dimensional fabric layers can be draped or wound onto a formhaving a surface reproducing the desired geometry of an inner or outersurface of the nozzle to be made in order to obtain the impregnatedpreform. Alternatively, the fibrous preform of the nozzle to be obtainedmay first be obtained and then this preform can be placed in aninjection cavity and then the polybenzoxazine monomer of formula C orthe mixture comprising this monomer described above injected into thecavity so as to impregnate the preform. In this case, a resin transfermolding technique can be used to impregnate the fibrous preform.

The invention also relates to a process for manufacturing an atmosphericreentry body in which the atmospheric reentry body is manufactured usinga crosslinked product obtained by the process described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a DSC thermogram of an example of a polybenzoxazine monomer offormula C obtained by carrying out the invention,

FIG. 2 is a result of thermogravimetric analysis (TGA) of a crosslinkedproduct obtained by crosslinking this polybenzoxazine monomer.

FIG. 3 is a DSC thermogram of another example of a polybenzoxazinemonomer of formula C obtained by carrying out the invention.

FIG. 4 is a thermogravimetric analysis result of a crosslinked productobtained by crosslinking this other polybenzoxazine monomer.

FIG. 5 is a DSC thermogram of an example of an additionalpolybenzoxazine monomer of formula E suitable for use in the context ofthe process according to the invention.

FIG. 6 is a thermogravimetric analysis result of a crosslinked productobtained by crosslinking this polybenzoxazine monomer.

DESCRIPTION OF THE EMBODIMENTS Examples Example 1: Synthesis of aPolybenzoxazine Monomer from Meta-Xylylene-Aminomethylphenol andBenzaldehyde and Subsequent Crosslinking

Meta-xylylenediamine is reacted with salicylaldehyde in stoichiometricproportions in methanol at reflux for 2 h to form the correspondingimine. The imine is reduced to the amine with 2 equivalents of NaBH₄added at 0° C. in a solution of the imine in ethanol, followed byheating at reflux for 2 hours. The meta-xylylene-aminomethylphenol thussynthesized is dissolved in toluene with 2 equivalents of benzaldehydeand then refluxed in a Dean-Stark apparatus to remove the watergenerated during condensation. After evaporation of the solvent underreduced pressure, the product obtained is a viscous liquid with anorange color when hot, and a pale yellow solid at room temperature. Theproduct was characterized by NMR and the structure was confirmed.

Thermal characterization by DSC revealed an enthalpy of polymerizationof 68 J/g. The DSC thermogram obtained is provided in FIG. 1.Thermogravimetric analysis of a crosslinked sample showed a coke contentof 57% under nitrogen atmosphere at 900° C. as well as a degradationtemperature of 10% of the total mass of 448° C. The thermogravimetricanalysis graph obtained is provided in FIG. 2 and shows good thermalstability and charring properties.

Example 2. Synthesis of a Polybenzoxazine Monomer from1,10-Decanediaminomethylphenol and Benzaldehyde and SubsequentCrosslinking

1,10-Diaminodecane is reacted with salicylaldehyde in stoichiometricproportions in methanol at reflux for 2 h to form the correspondingimine. The imine is reduced to the amine with 2 equivalents of NaBH₄added at 0° C. in a solution of the imine in ethanol, followed byheating at reflux for 2 hours. The 1,10-decanediaminomethylphenol thussynthesized is dissolved in toluene with 2 equivalents of benzaldehydeand then refluxed in a Dean-Stark apparatus to remove the watergenerated during condensation. After evaporation of the solvent underreduced pressure, the product obtained is a viscous liquid with anorange color when hot, and a pale yellow solid at room temperature. Theproduct was characterized by NMR and the structure was confirmed.

Thermal characterization by differential scanning calorimetry (DSC)revealed a melting temperature of 65° C. as well as an exothermicreaction between 209 and 260° C., representing 66 J/g of enthalpycompared with the reference, with a ramp of 20° C./min in high-pressuresealed steel crucibles. The resulting DSC thermogram is provided in FIG.3, Thermogravimetric analysis of a crosslinked sample showed a cokecontent of 46% under nitrogen atmosphere at 900° C. as well as adegradation temperature of 10% of the total mass of 404° C. Thethermogravimetric analysis graph obtained is provided in FIG. 4 andshows good thermal stability and charring properties.

Example 3: Study of a Mixture of a Polybenzoxazine Monomer SynthesizedPolyamine with an Additional Polybenzoxazine Monomer Synthesized from aPolyaldehyde

An additional polybenzoxazine monomer was synthesized from apolyaldehyde in the following manner.

Furfurylamine is reacted with salicylaldehyde in stoichiometricproportions in methanol at reflux for 2 h to form the correspondingimine. The imine is reduced to the amine with 1 equivalent of NaBH₄added at 0° C. in a solution of the imine in MeOH, followed by heatingat reflux for 2 h. The synthesized furfurylaminomethylphenol isdissolved in toluene with 0.5 equivalents of terephthalaldehyde andrefluxed in a Dean-Stark apparatus to remove water generated during thecondensation reaction. The reaction is stopped when the conversion ofaldehydes has reached its maximum, monitored by proton NMR. Afterevaporation of the solvent under reduced pressure, the isolatedbisbenzoxazine is an off-white solid. The product was characterized byNMR and infrared spectroscopy and the structure was confirmed.

Thermal characterization by differential scanning calorimetry (DSC)revealed a melting temperature of 150° C. as well as an exothermicreaction between 190 and 280° C., representing 261 J/g of enthalpycompared with the reference, with a ramp of 20° C./min in high-pressuresealed steel crucibles. The resulting DSC thermogram is provided in FIG.5.

A bisbenzoxazine sample was crosslinked at 180° C. for 4 hours andshowed no residual signal in DSC. Thermogravimetric analysis showed acoke content of 62% under nitrogen atmosphere, after 1 h at 900° C. aswell as a degradation temperature of 10% of the total mass of 403° C.(heating ramp: 20° C./min). The thermogravimetric analysis graphobtained is provided in FIG. 6. The crosslinked product obtained wasinsoluble in dichloromethane (the insolubility rate after 24 h at roomtemperature in dichloromethane, followed by drying under vacuum at 60°C. for 24 h was measured to be 100±0.1%).

The additional polybenzoxazine monomer synthesized from the polyaldehydewas mixed with the polybenzoxazine monomer obtained in Example 1. Theadditional polybenzoxazine monomer synthesized from the polyaldehydeadvantageously has a higher coke content when crosslinked compared withthe crosslinked polybenzoxazine of Example 1.

A mixture was made comprising the additional polybenzoxazine monomerobtained from polyaldehyde in an amount of 25% by mass and thepolybenzoxazine monomer synthesized from polyamine in an amount of 75%by mass. The mixture was heated to 80° C. using a water bath, then themixture was homogenized with a spatula and then crosslinked by heattreatment at 200° C.

Thermogravimetric analysis of this crosslinked mixture was performedunder nitrogen up to 900° C. The results are provided in Table 1 below.It can be noted that the tested polybenzoxazine mixture has anintermediate coke content between the products crosslinked from purepolybenzoxazines. The addition of the additional polybenzoxazine monomersynthesized from polyaldehyde increased the coke content. In Table 1below, the polybenzoxazine monomer synthesized from the polyamine isdenoted “bzx MXDA” and the additional polybenzoxazine monomersynthesized from the polyaldehyde is denoted “bzx TPA”. The mixture isalso suitable for application as an ablative resin for thruster nozzles.

TABLE 1 bzx MXDA/bzx TPA ratio Coke content at 900° C. T_(d) 10% 100/057% 448° C. 75/25 59% 411° C. 0/100 62% 405° C.

The expression “comprised between . . . and . . . ” should be understoodas including the bounds.

1. A process for manufacturing a polybenzoxazine monomer comprisingcondensing a polyamine of formula A with an aldehyde of formula B inorder to obtain the polybenzoxazine monomer of formula C, the chemicalformulas being provided below:

in these formulas: N₁ is an integer greater than or equal to 2; A₂ isselected from linear or branched, saturated or unsaturated, substitutedor unsubstituted hydrocarbon chains interrupted by one or moremonocyclic or polycyclic, substituted or unsubstituted, aromaticcarbocyclic or aromatic heterocyclic groups, or uninterrupted; informula A, the groups A₁ are identical or different and each have theabove formula A₁ with: R₁ ^(a) is selected from: electron-withdrawinggroups; saturated or unsaturated, substituted or unsubstituted, linearor branched hydrocarbon chains comprising between 1 and 6 carbon atoms,interrupted or not interrupted by one or more heteroatoms; saturated,unsaturated or aromatic, substituted or unsubstituted carbocyclic orheterocyclic groups; n^(a) is an integer comprised between 0 and 2;*-designates the bond to A₂; B₁ is selected from: monocyclic orpolycyclic, substituted or unsubstituted aromatic carbocyclic oraromatic heterocyclic groups.
 2. (canceled)
 3. The process as claimed inclaim 1, wherein A₂ is a substituted or unsubstituted xylylene group. 4.The process as claimed in claim 1, wherein n^(a) is equal to
 0. 5.(canceled)
 6. The process as claimed in claim 1, wherein B₁ is asubstituted or unsubstituted benzene ring.
 7. The process as claimed inclaim 1, wherein N₁ is an integer equal to
 2. 8. A process formanufacturing a crosslinked product comprising: manufacturing apolybenzoxazine monomer of formula C by carrying out the process asclaimed in claim 1, and crosslinking the polybenzoxazine monomer offormula C.
 9. The process as claimed in claim 8, comprising crosslinkingof a mixture comprising the polybenzoxazine monomer of formula C and anadditional monobenzoxazine monomer of formula D, formula D beingprovided below:

formula in which: R₁ ^(d) is selected from: substituted or unsubstitutedfurfuryl groups; saturated, unsaturated or aromatic, monocyclic orpolycyclic, substituted or unsubstituted carbocyclic or heterocyclicgroups; substituted or unsubstituted aralkyl groups; saturated orunsaturated, substituted or unsubstituted, linear or branchedhydrocarbon chains, interrupted or not interrupted by one or moreheteroatoms or by one or more saturated, unsaturated or aromatic,monocyclic or polycyclic, substituted or unsubstituted carbocyclic orheterocyclic groups; R₂ ^(d) is selected from: electron-withdrawinggroups; saturated or unsaturated, substituted or unsubstituted, linearor branched hydrocarbon chains comprising between 1 and 6 carbon atoms,interrupted or not interrupted by one or more heteroatoms; saturated,unsaturated or aromatic, substituted or unsubstituted carbocyclic orheterocyclic groups; n^(d) is an integer comprised between 0 and 2; D₁is selected from: saturated, unsaturated or aromatic, monocyclic orpolycyclic, substituted or unsubstituted carbocyclic or heterocyclicgroups; linear or branched, saturated or unsaturated, substituted orunsubstituted hydrocarbon chains, interrupted or not interrupted by oneor more heteroatoms.
 10. The manufacturing process as claimed in claim8, comprising crosslinking of a mixture comprising the polybenzoxazinemonomer of formula C and an additional polybenzoxazine monomer offormula E, formula E being provided below:

R₁ ^(e) is selected from: substituted or unsubstituted furfuryl groups;saturated, unsaturated or aromatic, monocyclic or polycyclic carbocyclicor heterocyclic groups; substituted or unsubstituted aralkyl groups;substituted or unsubstituted, linear or branched, saturated orunsaturated, substituted or unsubstituted hydrocarbon chains,interrupted or not interrupted by one or more heteroatoms; R₂ ^(e) isselected from: electron-withdrawing groups; saturated or unsaturated,substituted or unsubstituted, linear or branched hydrocarbon chainscomprising between 1 and 6 carbon atoms, interrupted or not interruptedby one or more heteroatoms; saturated, unsaturated or aromatic,substituted or unsubstituted carbocyclic or heterocyclic groups; n^(e)is an integer comprised between 0 and 2; E₁ is selected from: saturated,unsaturated or aromatic, monocyclic or polycyclic, substituted orunsubstituted carbocyclic or heterocyclic groups; linear or branched,saturated or unsaturated, substituted or unsubstituted hydrocarbonchains, interrupted or not interrupted by one or more heteroatoms; andN₂ is an integer greater than or equal to
 2. 11. A process formanufacturing a thruster nozzle comprising manufacturing the crosslinkedproduct by carrying out the process as claimed in claim 8 andmanufacturing the thruster nozzle with said crosslinked product.
 12. Aprocess for manufacturing an atmospheric reentry body comprisingmanufacturing the crosslinked product by carrying out the process asclaimed in claim 8 and manufacturing the atmospheric reentry body byusing said crosslinked product.
 13. The process as claimed in claim 3,wherein n^(a) is equal to
 0. 14. The process as claimed in claim 3,wherein B₁ is a substituted or unsubstituted benzene ring.
 15. Theprocess as claimed in claim 4, wherein B₁ is a substituted orunsubstituted benzene ring.
 16. The process as claimed in claim 3,wherein N₁ is an integer equal to
 2. 17. The process as claimed in claim4, wherein N₁ is an integer equal to
 2. 18. The process as claimed inclaim 6, wherein N₁ is an integer equal to 2.